The present invention relates generally to methods for continuously casting thin slabs or round ingots, and more particularly to a method for continuously casting thin slabs or round ingots that have a thickness of 8 to 40 mm from copper alloys, which tend to segregate during solidification.
When conventional casting methods are used, copper-nickel-tin alloys with higher nickel and tin concentrations, e.g. 15% nickel and 8% tin, in particular, tend to form considerable liquations during solidification. This causes segregations to occur at the grain boundaries, which segregations are heavily enriched with tin. Moreover, the cast structure is relatively coarse-grained, whereby the grain diameter lies in the centimeter range and the dendrite arms exhibit a relatively large spacing of about 100 .mu.m. On the other hand, it is desirable to have the most homogeneous structure possible with the least possible segregations, small grain diameters and small dendrite arm spacings. A casting structure that has considerable fluctuations in its composition, as caused by liquations, must be sufficiently homogenized before it can be shaped. Thus, it takes several weeks to anneal an unfavorable casting structure of a copper-nickel-tin alloy with about 15% nickel and 8% tin, for example for a homogenization treatment carried out at a temperature of about 900.degree. C.
As a general principle, it is known that as the duration and/or temperature of the annealing treatment increases, the structure of a material coarsens due to grain growth. However, grain coarsening further reduces the deformability of a material.
Methods for manufacturing bands of copper-nickel-tin alloys are generally known. For the most part, the known methods employ conventional casting material. This material is either cold-formed after the homogenization annealing or first homogenized and then cold-formed after hot-forming.
U.S. Pat. No. 4,373,970 (EP 0 079 755 B1) discloses a method for manufacturing strips of copper base spinodal alloy, e.g. copper-nickel-tin alloys, which method employs a powder-metallurgical technique to produce commercial products. Copper base spinodal alloys can for instance be produced in a powder metallurgy manner. Separate multiphase precipitations are formed by heat treatment, thus resulting in increased strength.
The present invention is directed to the problem of developing a casting method for continuously and thus economically manufacturing copper alloys, which have a strong tendency to segregate or which are difficult to shape, e.g. higher alloyed copper-nickel-tin alloys, without difficulties arising in the subsequent processing of the casting strands into bands, bars or wires.